1. Field of the Invention
Embodiments disclosed herein generally relate to blowout preventers used in the oil and gas industry. Specifically, embodiments selected relate to an improved packing unit for use in an annular type blowout preventer.
2. Background Art
Well control is an important aspect of oil and gas exploration. When drilling a well, for example, in oil and gas exploration applications, safety devices must be put in place to prevent injury to personnel and damage to equipment resulting from unexpected events associated with the drilling activities.
Drilling wells in oil and gas exploration involves penetrating a variety of subsurface geologic structures, or “layers.” Occasionally, a wellbore will penetrate a layer having a formation pressure substantially higher than the pressure maintained in the wellbore. When this occurs, the well is said to have “taken a kick.” The pressure increase associated with the kick is generally produced by an influx of formation fluids (which may be a liquid, a gas, or a combination thereof) into the wellbore. The relatively high pressure kick tends to propagate from a point of entry in the wellbore uphole (from a high pressure region to a low pressure region). If the kick is allowed to reach the surface, drilling fluid, well tools, and other drilling structures may be blown out of the wellbore. These “blowouts” may result in catastrophic destruction of the drilling equipment (including, for example, the drilling rig) and substantial injury or death of rig personnel.
Because of the risk of blowouts, blowout preventers (“BOPs”) are typically installed at the surface or on the sea floor in deep water drilling arrangements to effectively seal a wellbore until active measures can be taken to control the kick. BOPs may be activated so that kicks are adequately controlled and “circulated out” of the system. There are several types of BOPs, one common type of which is an annular blowout preventer.
Annular BOPs typically comprise annular, elastomeric “packing units” that may be activated to encapsulate drillpipe and well tools to completely seal about a wellbore. In situations where no drillpipe or well tools are within the bore of the packing unit, the packing unit can be compressed to such an extent that the bore is entirely closed, acting as a valve on the wellbore. Typically, packing units are used in the case of sealing about a drillpipe, in which the packing unit can be quickly compressed, either manually or by machine, to effect a seal about the pipe to prevent a well from blowing out.
An example of an annular BOP having a packing unit is disclosed in U.S. Pat. No. 2,609,836, (“Knox”) and incorporated herein by reference in its entirety, the assignee of the present invention. The packing unit includes a plurality of metal inserts embedded in an elastomeric body. The metal inserts are typically spaced equal radial distances from one another about a longitudinal axis of the packing unit. The inserts provide structural support for the elastomeric body when the packing unit is radially compressed to seal against the well pressure. Upon compression of the packing unit about a drillpipe, or upon itself, to seal against the wellbore pressure, the elastomeric body is squeezed radially inward, causing the metal inserts to move radially inward as well.
FIG. 1A is an example of a prior art annular BOP 101 including a housing 102. The annular BOP 101 has a bore 120 extending therethrough and is disposed about a longitudinal axis 103. A packing unit 105 is disposed within the annular BOP 101 about the longitudinal axis 103. The packing unit 105 includes an elastomeric annular body 107 and a plurality of metallic inserts 109. The metallic inserts 109 are disposed within the elastomeric annular body 107 of the packing unit 105 and distributed at equal radial distances from one another about the longitudinal axis 103. The packing unit 105 includes a bore 111 concentric with the bore 120 of the BOP 101.
The annular BOP 101 is actuated by fluid pumped into opening 113 of a piston chamber 112. The fluid applies pressure to a piston 117, which moves the piston 117 upward. As the piston 117 moves upward, the piston 117 translates force to the packing unit 105 through a wedge face 118. The force translated to the packing unit 105 from the wedge face 118 is directed upward toward a removable head 119 of the annular BOP 101, and inward toward the longitudinal axis 103 of the annular BOP 101. Because the packing unit 105 is retained against the removable head 119 of the annular BOP 101, the packing unit 105 does not displace upward from the force translated to the packing unit 105 from the piston 117. However, the packing unit 105 does displace inward from the translated force, which compresses the packing unit 105 toward the longitudinal axis 103 of the annular BOP 101. In the event a drill pipe is located along the longitudinal axis 103, with sufficient radial compression, the packing unit 105 will seal about the drill pipe into a “closed position.” The closed position is shown in FIG. 2B. In the event a drill pipe is not present, the packing unit 105, with sufficient radial compression, will completely seal the bore 111.
The annular BOP 101 goes through an analogous reverse movement when fluid is pumped into opening 115 of the piston chamber 112, instead of opening 113. The fluid translates downward force to the piston 117, such that the wedge face 118 of the piston 117 allows the packing unit 105 to radially expand to an “open position.” The open position is shown in FIG. 2A. Further, the removable head 119 of the annular BOP 101 enables access to the packing unit 105, such that the packing unit 105 may be serviced or changed if necessary.
An example of the prior art packing unit 105 used in an annular BOP 101 is shown in FIG. 1B. As before, the packing unit 105 includes an elastomeric annular body 107 and a plurality of metallic inserts 109. The metallic inserts 109 are distributed equal radial distances from each other in the elastomeric annular body 107 of the packing unit 105. The packing unit 105 includes a bore 111. FIG. 1C shows an example of the prior art metallic insert 109, in which the metallic insert may be disposed within the elastomeric annular body 107 of the packing unit 105.
FIG. 2A shows an example of the prior art packing unit 105 in the open position, where the packing unit 105 is disposed within an annular BOP. As before, the packing unit 105 includes an elastomeric annular body 107 and a plurality of metallic inserts 109. The metallic inserts 109 are distributed equal radial distances from each other in the elastomeric annular body 107 of the packing unit 105. The packing unit 105 includes a bore 111. Further, a drill pipe 301 is located along the longitudinal axis 103 of the annular BOP. In the open position, the packing unit 105 does not compress to seal about the drill pipe 301. Therefore, a gap is formed between the elastomeric annular body 107 of the packing unit 105 and the drill pipe 301. The open position of an annular BOP is meant to allow pressure to pass through the annular BOP.
FIG. 2B shows an example of the closed position of the packing unit 105. In the closed position, the elastomeric annular body 107 is compressed to seal about the drill pipe 301, such that pressure is not allowed to pass through the annular BOP. In the event the packing unit 105 is sealing from a blowout, the BOP may seal against wellbore pressure from the blowout coming from below.
FIG. 3 is an example of a prior art spherical BOP 301 disposed about a longitudinal axis 103. FIG. 3 is taken from U.S. Pat. No. 3,667,721 (issued to Vujasinovic and incorporated by reference in its entirety). The spherical BOP 301 includes a lower housing 303 and an upper housing 304 releasably fastened together by a plurality of bolts 311. Typically, the housing members 303 and 304 have a curved, semi-spherical inner surface. A packing unit 305 is disposed within the spherical BOP 301 about the longitudinal axis 103. The packing unit 305 includes a curved, elastomeric annular body 307 and curved metallic inserts 309 to correspond to the curved, semi-spherical inner surface of the housing members 303 and 304. The metallic inserts 309 are then distributed equal radial distances from one another within the curved, elastomeric annular body 307. The spherical BOP 301 may be actuated by fluid, similar to the annular BOP 101 of FIG. 1A as described above.
Increased demand for higher pressure containment and longevity make continued improvements to packing units desirable.